Spring damper device between a wheel and the body of a motor vehicle

ABSTRACT

A spring damper device is arranged between a wheel and a body of a motor vehicle. A damper cylinder and a piston rod co-operates with the latter. The damper device is directly articulatable between the body of the motor vehicle and a guide element of the wheel. A spring is tensioned between a body-side and a wheel-side abutment, and the clearance between the abutments is variable by a hydraulic adjusting device and measuring devices operable without contact therebetween to determine an installed length of the damper and clearance of the abutment for the spring. The damper and the spring extend coaxially, with the hydraulic adjusting device comprising a cylindrical housing configured to engage with an annular clearance around the piston rod and is sealed and guided radially at axial ends relative to this piston rod. The cylindrical housing is displaceable relative to the piston rod by hydraulic pressure acting on the annular space. The measuring devices are position-transmitters, one being fitted to the damping cylinder and another being fitted to the adjusting device. A sensor is fixedly connected to the piston rod being assigned to each position transmitter and are situated in a common tubular holder.

BACKGROUND OF THE INVENTION

This application claims the priority of German application 196 06 990.4and PCT/EP97/00796, filed Feb. 24, 1996 and Feb. 20, 1997, respectively,the disclosure of which are expressly incorporated by reference herein.

The present invention relates to a spring damper between a wheel and amotor vehicle body which includes a damper cylinder and a piston rodco-operating with the latter and is directly articulated between thebody of the vehicle and a guide element of the wheel, the spring istensioned between a body-side and a wheel-side abutment, the clearancebetween the abutments can be varied by a hydraulic adjusting device andin which measuring devices operating without contact are provided todetermine the installed length of the damper as well as the clearance ofthe abutment for the spring.

GB 2 288 577 A shows a shock absorber and spring disposed side by side,extending parallel to one another. The nature of the measuring device isnot described.

DE 35 02 579 A discloses a spring damper device of coaxial construction,having a device for adjusting the clearance of the abutments of thespring. Clearance measuring devices are not provided therein.

DE 42 44 204 A describes a shock absorber in which hydraulic fluid isdisplaceable by a displacement body from a damping cylinder via athrottle against an air cushion. The initial position of thedisplacement body in the damping cylinder, and thus the clearancebetween the articulations at the body and the guide of a wheel can bevaried by a separately possible variation of the hydraulic fluid flowwithin the damping cylinder.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a spring damping devicewhich, having a simple construction, also has a small dimensionperpendicular to the stroke direction and can operate with clearancemeasuring devices which are likewise of simple construction and can beaccommodated in space-saving fashion.

This object has been achieved by providing a spring damper device inwhich device having the damper and the spring extend coaxially, thehydraulic adjusting device comprises a cylindrical housing which engageswith annular clearance around the piston rod and is sealed and guidedradially at the axial ends relative to this piston rod, the housingbeing displaceable relative to the piston rod by hydraulic pressureacting on the annular space, the measuring devices comprise a positiontransmitter, one of which is fitted to the damping cylinder and one tothe adjusting device, a sensor fixedly connected to the piston rod beingassigned to each position transmitter, the sensors are situated in acommon tubular holder.

In accordance with the present invention, the sensors of the clearancemeasuring device are disposed, in a simple and reliably mounted mannerin design terms to lie one behind the other in a common tubular holder.This tubular holder can be disposed parallel to the piston rod of thevibration damper or may also be integrated into the piston rod, in thatthe piston rod itself forms the holder.

According to the present invention, the piston rod is advantageouslyintegrated into a hydraulic assembly to vary the clearance between thebody element and the guide element of a wheel of a motor vehicle. Theinstalled length of the vibration damper is altered by this hydraulicassembly, in that the piston rod is inserted more or less deeply intothe damping cylinder and oscillates relative to this adjustable positionduring travel. A common evaluation of the distance measuring systems setup according to the invention allows the respective clearance betweenthe articulations of the vibration damper on the vehicle body on the onehand and the guide element of an assigned wheel on the other hand to bedetermined unambiguously by way which are simple in terms of design andfunction, and specifically even when the piston rod is oscillating, overthe entire progression of the oscillation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-section view through a spring shockabsorber device, representing a spring leg of a motor vehicle, withradially internally disposed sensors of a distance measuring system; and

FIG. 2 is a longitudinal cross-section view of a spring shock absorberdevice similar to FIG. 1, but with radially externally disposed sensorsof a distance measuring system.

DETAILED DESCRIPTION OF THE DRAWINGS

The spring leg is arranged so as to be pivotable by universal jointswith a body-side joint 1 on a vehicle body (not illustrated) and with awheel-side joint 2 on a wheel guide element (likewise not illustrated),for example an axle.

In the spring leg, the damping cylinder 3 of the shock absorber adjoinsthe wheel-side joint 2, while the piston rod 4 of this shock absorber isconnected to the body-side joint 1. The piston rod 4 projects out of thedamping cylinder 3 over a relatively large area. In this area, ahydraulic adjusting device 5 acts on the piston rod 4. This hydraulicadjusting device 5 serves to vary the driving position of the vehicle orto adapt it to the respective current operating conditions. With such anadjusting device, in particular pitching and rolling movements orinclined positions of the vehicle body should be able to be compensatedautomatically. How this can take place specifically with a device ofthis type is described in detail, inter alia, in DE 42 31 641 A1, sothat it is not necessary to give further details of the relevant mode ofoperation here.

The adjusting device 5 has a cylindrical housing 7 as a movable elementto vary the volume of a hydraulic operating space 6. This housing 7 issealed at its axial ends relative to the piston rod 4 by annular seals 8for the sealed termination of the hydraulic operating space 6. The lowerone of these two seals 8 acts in an area of the piston rod 4 in whichthe latter has a first diameter up to a displacement piston 9 within thedamping cylinder 3. In contrast, the upper seal 8 engages around thepiston rod 4 in an area with a larger second diameter. The larger seconddiameter is achieved by a tubular sleeve 10 of the piston rod 4. Anannular gap 11 between the tubular sleeve 10 and the piston rod 4 lyingradially therein serves as a hydraulic fluid supply line to and from thehydraulic operating space 6. The annular gap 11 is connected via a line12 to a controlled hydraulic fluid store (not illustrated).

The clearance between the two joints 1, 2 is varied by displacementowing to a change in the volume of the hydraulic operating space 6. Whenthe volume of the hydraulic operating space 6 is kept constant, thecylindrical housing 7 of the hydraulic adjusting device 5 is operativelyfirmly connected to the piston rod 4. In this case, the vehicle bodyrests on the damping cylinder 3 of the shock absorber by connection tothe joint 1 via a spring 13. An annular collar 14 on the cylindricalhousing 7 constitutes the body-side abutment of the spring 13, while thewheel-side abutment is a bell-shaped annular collar 15 which is firmlyconnected to the upper end of the damping cylinder 3. If deflection orrebound of the spring 13 takes place when the adjusting device 5 isinactive, that is to say with the cylindrical housing 7 at rest relativeto the piston rod 4, only the damping cylinder 3 moves for vibrationdamping with the piston rod 4 practically at rest.

The cylindrical housing 7 of the hydraulic adjusting device 5 can bedisplaced between stops 16, 17 of the piston rod 4 by varying the volumeof the hydraulic operating space 6. In this area, the height of thevehicle body, that is to say the clearance between the two joints 1, 2,can thus be varied. To limit the oscillation amplitude of the shockabsorber, a further padded stop 25, which strikes against the dampingcylinder 3 when a predetermined amplitude has been reached, is providedon the piston rod 4 on the back of the stop 17. The stop 18, by way ofwhich deflection of the piston rod 4 in the direction of the dampingcylinder 3 is limited, serves to prevent the spring 13 falling below theblock size.

The above-described body is present in the same way in the twoembodiments shown in FIGS. 1 and 2. Differences exist only in the designof the distance measuring system.

In the embodiment according to FIG. 1, the piston rod 4 has a cavity 19over its entire length.

This cavity 19 is fitted with two sensors 21 (first sensor) and 20(second sensor). These sensors 20, 21 are configured as measuring coilswith a body according to DE 42 25 968 A1 which can be supplied withelectricity via a feed line 22 which is conducted out of the center ofthe piston rod 4. The sensors 20, 21 are each assigned positiontransmitters 23, 24 in the cylindrical housing 7 and at the open end ofthe damping cylinder 3. These position transmitters 23, 24 are aluminumrings which additionally fulfil the function of an axial closure of theoperating spaces of the hydraulic adjusting device 5, on the one hand,and of the damping cylinder 3, on the other hand. Here, the positiontransmitters 23, 24 have the function of a measurement object assignedin each case to the sensors 20, 21 configured as measuring coils in thesense of the distance measuring system device according to DE 42 25 968A1. In order to be able to use that known distance measuring system, thepiston rod 4 is made of a non-magnetizable material, such as for exampleceramic, aluminum, austenitic special steel or the like. The positiontransmitters 23, 24 are made of aluminum.

With a predetermined setting of the hydraulic device 5 remainingunchanged in relation to the active installed length of the vibrationdamper, the clearance of the vehicle body from an assigned guide elementof a wheel can be determined by the position transmitter 24.

In contrast, the axial assignment of the piston rod 4 relative to thecylindrical housing 7 of the hydraulic adjusting device 5 can bemeasured by the position transmitter 23.

By an evaluation of the positions of the position transmitters 23, 24,momentary actual clearances between the vehicle body and the roadsurface and the position of the housing 17 can be measured during traveleven with an active adjusting device 5, or changes in the clearance canbe determined continuously in terms of size.

The arrangement is also suitable in the same manner for the use ofmagnetostrictive sensors. Instead of the two measuring coils, thesensors 20, 21 consist of waveguides, and magnets are used as positiontransmitters 23, 24.

A particular advantage of the embodiment according to the presentinvention consists in being able to conduct the necessary sensorconnection cables out of the spring leg to the outside without anycontact to the hydraulic fluid within the device. Additionally, thesensor device of the measuring system accommodated in the piston rod 4is protected from environmental influences by the piston rod itself as ahousing for the sensor device. Moreover, the expenditure for assembly isconsiderably reduced compared to sensors mounted externally or inhydraulic fluid.

In the embodiment according to FIG. 2, the sensors 20, 21 of thedistance measuring system according to the embodiment in FIG. 1 arereplaced by sensors 120, 121 which are fitted radially externally of thepiston rod 104 but which are connected to the latter. In place of theposition transmitters 23, 24 which are shown in each instance in FIG. 1at the adjustable cylindrical housing 7 and at the damping cylinder 3,in the embodiment according to FIG. 2, the annular position transmitters123, 124 are fitted in each instance radially externally at theabovementioned parts. The function of the distance measuring system isin principle the same, despite the different assignment of the sensorsand position transmitters. The embodiment according to FIG. 2, havingelongate sensors 120, 121 lying radially externally of the piston rod104, is particularly advantageously suitable for short spring legs, inwhich the sensors cannot readily be accommodated in the piston rod 104,for reasons of space and strength.

In principle, the distance measuring systems described in theillustrative embodiments are advantageously usable in the case of allfeasible types of mutually telescopic connecting elements of variableclearance.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

We claim:
 1. Spring damper device configured to be arranged between awheel and a body of a motor vehicle, comprisinga damper cylinder and apiston rod co-operating with the latter, the damper device beingdirectly articulatable between the body of the motor vehicle and a guideelement of the wheel, a spring tensioned between a body-side and awheel-side abutment, the clearance between the abutments being variableby a hydraulic adjusting device and measuring devices operable withoutcontact therebetween to determine an installed length of the damper andclearance of the abutment for the spring, wherein the damper and thespring extend coaxially, the hydraulic adjusting device comprises acylindrical housing configured to engage with an annular clearancearound the piston rod and is sealed and guided radially at axial endsrelative to this piston rod, the cylindrical housing being displaceablerelative to the piston rod by hydraulic pressure acting on the annularspace, and the measuring devices comprise a position transmitter, onebeing fitted to the damping cylinder and another being fitted to theadjusting device, a sensor fixedly connected to the piston rod beingassigned to each position transmitter, the sensors being situated in acommon tubular holder.